1. Field of the Invention
This invention relates to a heavy-duty anticorrosion treatment of metal articles to be used in heavily corrosive environments.
2. Description of the Prior Art
Hitherto, metal articles to be used in heavily corrosive environments have been subjected to a heavy-duty anticorrosion treatment. More specifically, a metal article to be protected from corrosion is subjected to pre-treatment and then soaked in a plating bath containing a molten metal, such as zinc, to provide a coating of the metal on the surface of the article. It has been previously believed that the metal article thus treated should be cooled rapidly in a flow of water to prevent growth of a low-strength alloy layer which is formed at the interfacial boundary between the article and the metal coating. After such plating treatment, the plated article is heated for subsequent treatment, baked with a synthetic resin to provide a coating of the resin on the plated article, and then cooled with water to accomplish heavy-duty anticorrosion treatment.
The metal article thus treated has defects in that a fragile metallic layer grows at the boundary between the plated layer and the metal article and that surface oxidation on the plated layer occurs due to heating for the baking treatment, which result in deterioration in mechanical properties of the plated layer and also in deterioration in adhesion between the plated layer and the baked synthetic resin layer. Moreover, such conventional method requires additional heating apparatus for re-heating treatment before the baking.
Thus, an object of the present invention is to provide a process for heavy-duty anticorrosion treatment of metal articles to give anticorrosive metal articles having an excellent durability when used in a heavily corrosive environment.
Another object of the invention is to provide the above mentioned process which can be carried out efficiently with low cost.
Other objects and advantages of the invention will be apparent from the description given below.